Websites and web apps provide layouts of content in a manner chosen by a developer of the website or web app. Client browsers may allow users to statically configure preferences for display of content, and some websites allow users to customize a viewing environment for their specific services.
Most web layout schemes for a client are managed by cascading style sheet (CSS). CSS is primarily a style sheet language used to describe the look and formatting of a document written in a markup language such as hypertext markup language (HTML), extensible hypertext markup language (XHTML), extensible markup language (XML), scalable vector graphics (SVG), and XML user interface language (XUL). CSS is designed primarily to enable the separation of document content (written in HTML or a similar markup language) from document presentation, including elements such as the layout, colors, and fonts. To manage layout of a page requires complex hand coding of CSS.
Some code such as JavaScript can be used to detect client screen size and resolutions. The content delivery for that client can then be managed to display properly on the client screen.